The assignee of the present invention designs and develops voltage-fed induction machine drives comprising motors of electric vehicles. In electric vehicle or a hybrid electric vehicle applications, it is desirable that the drive system, comprising an inverter and an electric motor, operates under maximal efficiency. The drive system should also be capable of producing maximal torque achievable for a given inverter and machine voltage and current rating. This is especially difficult to achieve at lower DC link voltage values.
Example prior slip-control methods are optimized for steady-state operation, and the transient response to torque changes is generally slow, oscillatory, and not always monotonously increasing for a monotonously increasing torque command. Real-time efficiency control algorithms typically require complex signal processing, and typically have poor transient response, since the transient condition has to be identified, and the efficiency optimization algorithm turned off first, before responding to the increasing torque command. Consequently, conventional algorithms do not provide for maximal torque per ampere production at higher torque levels.
It would therefore be desirable to have an improved control algorithm for induction machine control that achieves the highest possible motor efficiency at the operating point. It would also be desirable to have an improved control algorithm for induction machine control that provides good transient response, and tracking of the torque command. It would also be desirable to have an improved control algorithm for induction machine control that provides for maximal efficiency control at low torque levels, and maximal torque per ampere control at high torque levels.